The present invention relates generally to the field of fuel delivery devices, and more particularly, is directed to a system and method for effecting either automatic or manual control of a fuel delivery system for delivering a variable quantity of fuel to the engine of a power delivery apparatus.
With the present emphasis in the automotive industry toward improving fuel economy and reducing exhaust emissions, there has been much research and development directed toward providing automatic systems for controlling the operation of a motor vehicle. Some of the research and development has focussed on systems for controlling the fuel delivered to the engine of the vehicle. One such system is disclosed in U.S. Pat. No. 4,424,785, issued in the name of Ishida et al. In this system, various parameters such as the degree of movement of the accelerator pedal, air flow within the engine intake bore and throttle valve position are provided to a control unit which compares these parameters with pre-programmed values to provide an optimum throttle valve setting for the engine. Should the control unit fail, however, the throttle cannot be controlled and the vehicle can not be run. Ishida recognized this deficiency and discloses an auxiliary control unit which assumes control over the throttle when the main control unit is out of order. When the main unit malfunctions, the auxiliary unit is immediately activated. The auxiliary unit, however, provides only limited throttle control, sufficient only to drive the vehicle at low speed to a service station to effect repair of the main unit.
While the Ishida system represents an improvement over such systems known in the prior art, his system is also deficient. For example, in Ishida, the auxiliary control unit immediately assumes control of the throttle valve when the main unit malfunctions. No provisions are provided for returning the throttle valve to a predetermined position or ascertaining the position of the throttle valve so that control can be smoothly passed to the auxiliary unit. Thus, the vehicle may lurch forward or stall until the throttle valve setting matches the auxiliary control unit demand. Moreover, in the Ishida system, the auxiliary control unit provides only limited throttle operation. Thus, the vehicle may be operated only at low speeds until the main unit is repaired. Restricting the vehicle to low speed operation can be dangerous in some situations, as for example freeway driving. It can also be dangerous during routine city driving as well as traffic conditions often demand rapid acceleration. Thus, while Ishida represents an improvement over prior fuel delivery control systems, it is not the ideal system.